Selective reconfiguration of layer 4 visual cortical circuitry by visual deprivation.

Visual deprivation during a developmental sensitive period markedly alters visual cortical response properties, but the changes in intracortical circuitry that underlie these effects are poorly understood. Here we use a slice preparation of rat primary visual cortex to show that 2 d of prior visual deprivation early in life increases the excitability of layer 4 circuitry. Slice recordings showed that spontaneous activity of layer 4 star pyramidal neurons increased 25-fold after 2 d of visual deprivation between postnatal days (P) 15 and P17. This effect was mediated by increased net excitatory and decreased net inhibitory synaptic drive. Paired recordings showed that excitatory connections between star pyramidal neurons doubled in amplitude, whereas inhibitory connections decreased or increased depending on the interneuron class. These effects reversed when vision was restored. This dynamic adjustment of the excitation-inhibition balance may allow the networks within layer 4 to maintain stable levels of activity in the face of variable sensory input.